Yamaha 40 2-stroke........did i damage my motor with seafoam????

[mitzi16]

First off this is my first post, so thank you for allowing into this site.
A little history with what I am dealing with.

A just bought a used 2005 Yamaha 40 2-stroke with oil injection on a Mitzi Skiff 16 flats boat. The motor maybe has 200 hours on it....max.

The boat had been sitting up for about 6 months before I bought it.

Before I took it out....I removed the fuel tank and drained it and flushed it out good with my pressure washer and then filled it up with water to "float" any debris that might be in it........emptied it out and let it air dry for 10 days (to make sure it was completely dry) before refueling.........

I filled it (12 gallon tank) with 93 octane and a 16oz can of seafoam.

replaced the fuel water seperator and inline fuel filter and the filter on the motor itself....so fuel is being filtered 3 times before it makes it into the fuel pump.

on my maiden voyage.....it cranked right up at the ramp....like a brand new motor...idled smooth and quiet...i backed it off the trailer and putted around the dock for a few minutes while the truck was being parked.

about 5 minutes goes by....my buddy gets in and we go to take off, and when i go to give it gas it chokes down.....fires right back up.....give it gas....same thing...chokes down.

i figured there was gunk in the carbs so, i would just keep idling around and let the fresh gas and seafoam go to work....a few minutes later it straightens right up and off we go.....running like a scalded cat. we ran all over the place..stopping to fish here and there...it would crank up on the first revolution everytime and haul *****. finally after running it for a few hours we took it home....rinsed out the motor and put it away.

6 days go by.....i go to put it in the weekend and it fired right up ...... like a new motor...it's kind of scary how quick this thing starts......

i leave the motor running while i go park the truck...come back and get in and it is still idling just as quiet and smooth as you could ask.......go to plane off and it will only do 3,000 rpm and barely on plane.....running smooth mind you - just no power......

i can take it out of gear and rev it up with the warm up lever with no problem.....but when i go to put a load behind it with the prop it wouldn't do more than 3,000.......so i eased to some docks to fish. when i went to crank it up to go back home......it would only idle in gear....no more than 800 rpm's....anything more and it would choke down.

me and my friend who use to own a high performance mercury racing shop in Charleston 30 years ago went through the crabs....all jets were clean as a whistle.....replaced spark plugs.....put it back in to try it....same thing......would idle up and rev it with the warm up lever,,,,,but put it in gear and it just won't do more than 3,000.....no power.

now that we have eliminated the carbs, plugs, bad gas, no sucking air anywhere.......did i burn a piston with the seafoam do you think? I will be doing a compression test when i get home this afternoon to hopefully rule that out.

Bad coil? Fuel pump?

any ideas?

mind you it still cranks on the first revolution and idles smooth and quiet and revs great....as long as it is not under a load in gear.

thanks in advance.

[99yam40]

If it has good compression in all cylinders , then check the spark with a spark tester or with a inductive timing light on the different plug wires to make sure it is not dropping spark at the problem RPM. Also check to see if the timing is advancing as it should.
Almost sounds like timing not advancing or it is in the safe mode do to low oil level or high temperature. Does your alarm work?
If all that is good then it is a fuel problem, I would think it was the carbs but not if it runs smooth as any cylinder that is not firing properly should cause it to run rough. could be fuel pump or sucking air. easy to test with a fuel pressure/vacuum gauge

[yamatech43]

Don't care if the guy owned a shop or twenty....is he a master tech? Then he knows those yama carbs have to be soaked overnight in REAL carb cleaner, nothing out of a spray can....and the jets are seldom what is clogged....classic carb symptoms....they'll run smooth sometimes, depending on what is happening in carb....if it'll only idle smoothly then clean the carbs....may have to do this several times from gunk in lines on motor from sitting. worst thing for a two stroke is to sit.

[mitzi16]

carbs are perfect, compression is perfect............ended up being a bad spark plug wire. fixed and running like a champ now.

[99yam40]

good to hear you found your problem.
Did you find it by testing spark or just ohming out the wires?

[mitzi16]

testing the spark.

[199675hpforce]

So how did you test if spark was not there? Without the proper tools there is no way to check except timing light, grounding the spark plug to block is only thing I can think of. Not grounding the wire when cranking can damage the cdi packs

First off this is my first post, so thank you for allowing into this site.
A little history with what I am dealing with.

A just bought a used 2005 Yamaha 40 2-stroke with oil injection on a Mitzi Skiff 16 flats boat. The motor maybe has 200 hours on it....max.

The boat had been sitting up for about 6 months before I bought it.

Before I took it out....I removed the fuel tank and drained it and flushed it out good with my pressure washer and then filled it up with water to "float" any debris that might be in it........emptied it out and let it air dry for 10 days (to make sure it was completely dry) before refueling.........

I filled it (12 gallon tank) with 93 octane and a 16oz can of seafoam.

replaced the fuel water seperator and inline fuel filter and the filter on the motor itself....so fuel is being filtered 3 times before it makes it into the fuel pump.

on my maiden voyage.....it cranked right up at the ramp....like a brand new motor...idled smooth and quiet...i backed it off the trailer and putted around the dock for a few minutes while the truck was being parked.

about 5 minutes goes by....my buddy gets in and we go to take off, and when i go to give it gas it chokes down.....fires right back up.....give it gas....same thing...chokes down.

i figured there was gunk in the carbs so, i would just keep idling around and let the fresh gas and seafoam go to work....a few minutes later it straightens right up and off we go.....running like a scalded cat. we ran all over the place..stopping to fish here and there...it would crank up on the first revolution everytime and haul *****. finally after running it for a few hours we took it home....rinsed out the motor and put it away.

6 days go by.....i go to put it in the weekend and it fired right up ...... like a new motor...it's kind of scary how quick this thing starts......

i leave the motor running while i go park the truck...come back and get in and it is still idling just as quiet and smooth as you could ask.......go to plane off and it will only do 3,000 rpm and barely on plane.....running smooth mind you - just no power......

i can take it out of gear and rev it up with the warm up lever with no problem.....but when i go to put a load behind it with the prop it wouldn't do more than 3,000.......so i eased to some docks to fish. when i went to crank it up to go back home......it would only idle in gear....no more than 800 rpm's....anything more and it would choke down.

me and my friend who use to own a high performance mercury racing shop in Charleston 30 years ago went through the crabs....all jets were clean as a whistle.....replaced spark plugs.....put it back in to try it....same thing......would idle up and rev it with the warm up lever,,,,,but put it in gear and it just won't do more than 3,000.....no power.

now that we have eliminated the carbs, plugs, bad gas, no sucking air anywhere.......did i burn a piston with the seafoam do you think? I will be doing a compression test when i get home this afternoon to hopefully rule that out.

Bad coil? Fuel pump?

any ideas?

mind you it still cranks on the first revolution and idles smooth and quiet and revs great....as long as it is not under a load in gear.

thanks in advance.

[Silvertip]

See how easy it is to blame something (SeaFoarm in this case) for a problem that is not related to it. Uninformed "techs" tend to do just that before doing any real diagnostic work.